Supercooling means the phenomenon that a molten object or a solid is not changed although it is cooled to a temperature below the phase transition temperature in an equilibrium state. A material has a stable state at every temperature. If the temperature is slowly changed, the constituent elements of the material can follow the temperature changes, maintaining the stable state at each temperature. However, if the temperature is suddenly changed, since the constituent elements cannot be changed into the stable state at each temperature, the constituent elements maintain a stable state at an initial temperature, or some of the constituent elements fail to be changed into a state at a final temperature.
For example, when water is slowly cooled, it is not temporarily frozen at a temperature below 0° C. However, when water enters a supercooled state, it has a kind of quasi-stable state. As this unstable equilibrium state is easily broken even by slight stimulation, water tends to move into a more stable state. That is, if a small piece of the material is put into the supercooled liquid, or if the liquid is suddenly shaken, the liquid starts to be frozen at once such that its temperature reaches the freezing point, and maintains a stable equilibrium state at the temperature.
In general, an electrostatic atmosphere is made in a refrigerator, and meat and fish are thawed in the refrigerator at a minus temperature. In addition to the meat and fish, fruit is kept fresh in the refrigerator.
This technology uses a supercooling phenomenon. The supercooling phenomenon indicates the phenomenon that a molten object or a solid is not changed although it is cooled to a temperature below the phase transition temperature in an equilibrium state. In the prior art, an electric field or magnetic field is applied to the stored object to be cooled such that the stored object enters a supercooled state. Accordingly, a complicated apparatus for producing the electric field or magnetic field should be provided to store the stored object in the supercooled state, and the power consumption is increased during the production of the electric field or magnetic field. Additionally, the apparatus for producing the electric field or magnetic field should further include a safety device (e.g., an electric field or magnetic field shielding structure, an interception device, etc.) for protecting the user from high power, when producing or intercepting the electric field or magnetic field.
Japanese Patent Publication No. 2001-4260 describes a supercooling control refrigerator which includes a temperature detection means and a control means controlling the temperature at a given set temperature in an openable/closable insulation unit and which keeps the goods cold at a temperature below the freezing point during the supercooling operation. However, since the refrigerator controls the rotation number of a cool air circulation fan to adjust the temperature in the insulation unit, if the temperature in the unit is reduced to a temperature below the set temperature, there is no means for raising the temperature to the set temperature within a short time. When the temperature in the unit is maintained at a temperature below the set temperature for a predetermined time, the goods intended to be stored in a supercooled state are frozen. In addition, the frozen goods cannot be thawed and stored again in the supercooled state. The refrigerator has low stability in maintaining a non-frozen state.
Korean Registered Patent No. 10-850062 describes a refrigerator having a space for storing food and a storing room for cooling the space, the refrigerator including a cool air flowing space directly cooling the food storing space and an insulation layer insulating the cool air flowing space from the space, and storing the food in a supercooled state. However, if the temperature in the refrigerator is reduced to a temperature below a set temperature, there is no construction for raising the temperature. Therefore, the refrigerator also has low stability in maintaining a non-frozen state.
Japanese Patent Publication No. 2008-267646 describes a refrigerator with a supercooling room which includes a freezing chamber with a temperature control means therein to continuously adjust the temperature between 0° C. and a temperature of a freezing temperature zone by stages, the supercooling room disposed in the freezing chamber and receiving the cool air from the freezing chamber, and a control apparatus controlling the freezing chamber so that the food stored in the supercooling room can be maintained in a supercooled state at a temperature below the freezing point without being frozen. The temperature of the freezing chamber or a switching chamber in which the supercooling room is installed is controlled to adjust the temperature of the supercooling room. The supercooling room is sealed with respect to the freezing chamber or the switching chamber such that a temperature change in the supercooling room is limited. However, when the food is stored in the supercooled state by slowing down the temperature change in the supercooling room by indirect cooling, it takes a long time for the food to reach the supercooled state. Moreover, if the temperature in the refrigerator is reduced to a temperature below a set temperature, there is no construction for raising the temperature. Accordingly, the refrigerator also has low stability in maintaining a non-frozen state.